The invention relates generally to a roller for the pressure treatment of a continuous web of material and more specifically to an improved device for limiting the displacement of the roll cylinder in a hydraulically supported roller.
German Patent No. 22 30 139 discloses a transversely controlled, hydraulically supported roller in which several supporting plungers, arranged in a row on the cross-head along the side of the roller adjacent the roll gap, can independently be pressurized with pressure fluid. In this manner, the supporting plungers function to provide predetermined counteracting forces that act against the inner circumference of the outer roll cylinder to produce a specific line pressure distribution whereby the cross-head, under the influence of the counteracting forces, can bend inside the cylinder.
While the cylinder disclosed in German Patent No. 22 30 139, is supported at its ends by the cross-head, German Patent No. 22 54 392 discloses a roller having a so-called "internal stroke" whereby the cylinder can move radially opposite the cross-head. At the roll ends, the cylinder is only supported by a guide ring, which can be displaced radially opposite the cross-head.
In hydraulically supported rolls of the above-described types, the cross-head takes up most of the interior space of the cylinder. Therefore, only a small radial displacement path is available for the cross-head to bend. When a certain displacement is exceeded, damage can occur. This damage can be avoided by limiting the stroke of the supporting plungers.
In the case of first-described rollers, in which the cylinders are supported at their ends by the cross-head, no relative radial displacement of the cross-head and cylinder takes place at the extremities. Displacement can only occur at the middle of the roller, where the cross-head, as a result of the deflection, bends to the other side of the roller opposite the direction of the force of the central supporting elements. However, in the case of the second-described rollers that have an "internal stroke", the cross-head can move over its entire length.
The damage that can occur when the displacement is too great is brought about when the outer bending side of the cross-head contacts the inner circumference of the cylinder. In this manner, the surface at the inner circumference of the cylinder may be damaged. Damage also can result, if a supporting plunger extends too far out of its cylinder recess. Finally, in the case of rollers with an "inner stroke", the mating rolls or corresponding elements supported by the roller may be shifted to an extent that is harmful.
Previous attempts to solve this problem involve retaining the cross-head in a desired nominal position. For example, in German Pat. No. 30 26 865, the position of the outer roll shell or cylinder is measured relative to the cross-head, and the pressure fluid applied to the individual supporting elements is controlled accordingly. The roller disclosed in German Pat. No. 28 49 253 functions in a similar manner. This roller has an "inner stroke" and includes a valve arranged between the guide ring and the cross-head. The valve allows the pressure in the supply line to the individual supporting elements to fall when a specific displacement between the cross-head and the cylinder becomes too great.
All of these previously attempted solutions, in addition to being costly, involve controlling the pressure supplied to the supporting elements by means of controlled valve arrangements. Therefore, the security of the safe operation of these apparatus can only be as effective as the operability of the valve arrangements they employ.
The invention is directed to the problem of achieving a simpler and more secure stroke limitation in hydraulically supported rollers.